The present invention relates generally to pistons and more specifically, to an improved diaphragm piston.
Diaphragm pistons, for example, for use in a service portion of a rail pneumatic brake valve, for example, a DB-60 brake valve available from New York Air Brake Corporation, is illustrated in FIGS. 1 and 2. The diaphragm piston includes a rubber diaphragm 24 held between a body 20 and a plate 28 which is secured together by a post 10 having a head 12 and a threaded portion 16 which receives a nut 34. A spring 36 is positioned between a spring seat 38 and the back side of the plate 28. A retainer 40, secured to the post 10 by C-ring 42, acts as a stop for the spring seat 38. A stem 45 is inserted into and is secured to post 10 by aligning orifices 19 and 46 and pin 47. Stem 45 is received and guided in a bushing of a valve seat (shown in phantom). The stem 45 includes a shoulder 44 which can catch and wear the valve seat bushing.
Other than the rubber diaphragm 24, all of the parts are metal. In that all of the parts are metal, the post 10 requires processing to create the different areas, including the threading. The number of parts increase the expense of the diaphragm piston. Also, there is no mechanism to prevent rotation of the elements relative to each other.
The present invention is a diaphragm piston having a diaphragm between a body and plate. A post integral with and extends from the body through the diaphragm and the plate. A stop is coupled to the post and limits the axial movement of the plate away from the body. A spring seat is coupled to the post. A spring is between the plate and the spring seat. The post includes a first shoulder and the stop engages the first shoulder. The stop includes an orifice shaped to move axially on the post past the first shoulder and rotate about the post and engage the first shoulder. The first shoulder has at least one circumferential recess and the orifice in the stop includes a radial tab smaller than the recess.
A first lock prevents rotation between the stop and the post. The lock includes a recess on both the stop and the plate and a key is inserted in the recess when aligned. The spring retains the key in the recess. A second lock is also provided preventing rotation between the plate and post. The second lock includes at least one pin and a recess, one of which is on the plate and one of which is on the body.
The post includes a second shoulder and the spring seat engages the second shoulder. The spring seat includes an orifice shape to move axially on the post past the second shoulder and rotate about the post and engage the second shoulder. The second shoulder for the spring seat includes a first portion having a generally first polygonal shape and a second portion having a generally second polygonal shape of more sides than the first shape. The orifice in the spring seat is shaped to move axially past the first portion of the second shoulder and rotate about the post and engage the second portion of the second shoulder. Preferably, the first polygonal shape is generally a triangular shape and the second polygonal shape is generally an hexagonal shape.
A unique relationship between the piston guide stem and valve seat is provided. A guide is integral with and extends from the body in a direction opposite from the direction the post extends from the body. A stem is loosely seated in an orifice of the guide. The stem includes a uniform diameter, with circumferentially spaced flats, which maintains guiding contacts with a bushing of a valve seat over the total travel of the piston.
Whereas the diaphragm is rubber, the body, the plate and the lock that prevents rotation between the stop are all made of plastic. The stem, spring seat and the spring are made of metal.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.